Still, I suspect that your teacher would have objected to a criticism in the form of

"what is it in your brain that makes you think it doesn't suck?"

Our guest is not critiquing, ze is just putting down Derek.

Adam, I disagree. There is nothing wrong with being unsupportive of nasty comments. This is a place for us to be supportive of artistic efforts, not everything anybody does. You were unsupportive of a cowardly putdown. And that's not something to apologize for.